SCHEDULE 13G/A

Y-MABS THERAPEUTICS INC

Common stock, par value $0.0001 per share · CUSIP: 984241109

Event date: 2025-08-19

Reporting persons may disclose overlapping interests. Their amounts are shown individually and are not added into a filing total.

Filing-level shares

Unavailable

Percent of class

Unavailable

• ACORN BIOVENTURES, L.P.

  Shares: 1,175,686.00 · Class: 2.6%

• ACORN CAPITAL ADVISORS GP, LLC

  Shares: 1,175,686.00 · Class: 2.6%

• ACORN BIOVENTURES 2, L.P.

  Shares: 1,620,611.00 · Class: 3.6%

• Acorn Capital Advisors GP 2, LLC

  Shares: 1,620,611.00 · Class: 3.6%

• Anders Hove

  Shares: 2,796,297.00 · Class: 6.2%

Amounts are as disclosed in this filing. Schedule type alone does not establish investment intent.